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1. Open Terminal



2. 
   

   Enter the following command:

   
   
   

   cat /sys/class/backlight/intel_backlight/brightness
   
   

   
   



3. Write down the resulting value (12421 in my case)




4. Divide value by 6 and write it down (2070 in my case)



5. 
   

   Enter the following in the terminal, replacing 2070 with your value:

   
   
   

   sudo su -c "echo 2070 >/sys/class/backlight/intel_backlight/brightness"
   
   

   
   



6. Close Terminal




7. For future usage of the last command, open Terminal, press Ctrl and R together, start typing brightness. When the last command appears, just press Enter.

It works for me on a Samsung NC110 with Ubuntu 12.04.

None of the answers here worked for me (on a Dell Precision 5510). The output from cat /sys/class/backlight/intel_backlight/brightness for me was 1 and setting it any lower completely turned the screen off.

I finally found a solution from the answer here:

xrandr --output eDP1 --brightness .3

I was also able to get this to work on my external monitor (attached via a display port dock), and reduce it below the minimum brightness allowed by the hardware controls on the monitor:

xrandr --output DP1-1 --brightness .6

Note that your display might not be eDP1 (or DP1-1), but you can list all available displays by hitting tab twice after --output, or from xrandr -q which shows which ones are currently connected. Tweak the value for brightness, i.e., .4, .5, etc until you find a level that works for you.

Try to override the min brightness manually with

1. sudo nano /sys/class/backlight/acpi_video0/brightness




2. Change the value in this file to 0 (clear and type 0 if value is already 0).




3. Press Ctrl + X to exit.




4. Press Y and Enter to save the file.

This works for me. You can also try sudo sh -c 'echo 0 > /sys/class/backlight/acpi_video0/brightness'

I am still looking for a more robust approach. Any help is appreciated.

I'm not using Ubuntu but Debian, but sometimes (second screen plugin, gnome restart) the brightness drops to zero. So I've created an inotify enabled application (it consumes zero cputime while there is no change in brightness) and when there is the change and it is changed to zero (or lower some predefined level, which you can specify) it sets the brightness to some default level, which you can also specify.

Please find it at my github page: https://github.com/nuccy/zero_brightness_fixer

This tool is a slider utility to set /sys/class/backlight/intel_backlight/brightness:

• https://github.com/oblitum/backlight

Works for my intel based MacBook Pro.

Install xbacklight by typing the following in the terminal

sudo apt-get install xbacklight

then:

xbacklight -percentage

replace the word "percentage" with the number of your choice to decrease the backlight from 1 to 99. In contrast, you can also do:

xbacklight +percentage 

to increase the brightness by replacing the word "percentage" with a number between 1 and 100. For more information, run the following in the terminal:

xbacklight -help

I know that this is probably too late, but I hope it helps :)

This app works for me for decreasing brightness well beyond the usual https://github.com/lordamit/Brightness